Medical devices such as guide wires and various catheters, which have been hitherto used by being inserted or pierced into a living body, have a surface formed of a resin such as silicon resin, polyurethane, and vinyl chloride resin. When the medical device having a tubular or rod-shaped configuration provided with such a surface is inserted into the body, it is difficult to make insertion because of an extremely large frictional resistance. Therefore, problems arise, for example, in that the living body suffers from a great deal of pain, and mucous membrane and tissue are damaged.
In order to obviate on the foregoing drawbacks, it is known that the surface of the medical device as described above is treated such that a low friction material such as a fluororesin is used therefor, or a hydrophilic macromolecule or a lubricant such as Xylocaine jelly and olive oil is applied thereto. However, even when fluororesin is used, the friction is not sufficiently reduced when the medical device is inserted into the living body. When the lubricant is applied, the lubricant flows out within an extremely short period of time. Therefore, it is impossible to obtain a sufficient effect.
Taking notice of the fact that the hydrophilic high-molecular compound swells in the presence of an aqueous medium, and the coefficient of friction is decreased in accordance therewith, Japanese Laid-Open Patent Publication No. 6-7426 discloses that the surface of a medical device is coated, for example, with a polymer composed of maleic anhydride. However, in this method, the surface of the medical device is merely coated with the water-soluble macromolecule. Therefore, the hydrophilic macromolecule tends to be eluted from the surface, which is not desirable from a viewpoint of safety. Further, the effect to reduce the friction does not continue for a long period of time.
Japanese Laid-Open Patent Publication No. 3-184557 discloses that a hydrophilic vinyl monomer is graft-copolymerized on a surface layer of a medical device. In this method, the improvement is made in that the elution of the water-soluble macromolecule is suppressed, however, a product obtained by the graft polymerization does not have a high molecular weight. Therefore, it is impossible to obtain a sufficient effect to decrease the friction.
Each of Japanese Laid-Open Patent Publication Nos. 54-29343 and 58-193767 discloses a medical device coated with an N-vinylpyrrolidone polymer by the aid of an isocyanate group. However, a problem of elution of the polymer also arises.
Japanese Laid-Open Patent Publication No. 63-238170 discloses a medical device in which a copolymer composed of an active hydrogen-containing monomer and N-vinylpyrrolidone is coupled to a base material through an isocyanate group, and Japanese Patent Publication No. 1-33181 discloses a medical device in which a copolymer composed of maleic anhydride and methyl vinyl ether is coupled to a base material through an isocyanate group. The improvement is made from a viewpoint of elution, because these compounds form chemical bonds. However, the copolymer composed of maleic anhydride and methyl vinyl ether is hydrolyzed upon contact with water. As a result, maleic acid is produced from maleic anhydride, and the surface of the medical device becomes extremely strongly anionic. Therefore, the compound is not preferred from a viewpoint of biocompatibility. Further, the hydrophilic property is insufficient, and it is impossible to expect a sufficient effect to reduce the friction, because methyl vinyl ether which is not hydrophilic is contained in an amount of 50%. Both of the copolymer composed of the active hydrogen-containing monomer and N-vinylpyrrolidone and the copolymer composed of maleic acid and methyl vinyl ether have low flexibility, and hence they have low film strength. Accordingly, they have a drawback that the surface is easily peeled off when it undergoes friction.
As described above, the conventional method has failed to provide a medical material in which the coefficient of friction is safely reduced while suppressing the elution of macromolecule existing on the surface of the base material.